About difference boundaries

Difference boundaries are zones of rapid change. BoundarySeer delineates difference boundaries through wombling methods, including wombling with location uncertainty and wombling on fuzzy classes, as well as using classification entropy and confusion index as Boundary Likelihood Values for fuzzy classes.

The following icons represent difference boundaries in the project window:

diff.gif

polybound.gif

rasterbound.gif

point

polygon

raster

For difference boundaries, boundary information can include (1) Boundary Likelihood Values; (2) gradient angle values; (3) Boundary Element (BE) designations; (4) Boundary Membership Values; and (5) subboundaries (connected boundary elements). To view these values, go to the "Project" menu, select "Table" and choose the boundary table. Alternatively, you can right-click on the boundary icon in the project window and choose "View Table".

  1. Boundary Likelihood Values (BLVs) measure the degree of change in raster or point data, or calculated distance metrics in transect or polygon data. For categorical data, BLVs are based on mismatch values.

  2. Gradient angles are the direction of the maximum change in the BLV at a specific location. The angle is calculated relative to a horizontal vector pointing east from the candidate BE. Two adjacent boundary elements are connected to form a subboundary only if the average differences in their aspects and their connection angle with the subboundary (see diagram) are within thresholds set by the user. Gradient angles are calculated in wombling on numeric point or raster data.

  3. Boundary elements (BEs) compose a difference boundary. BEs are a set of locations associated with large amounts of change in the underlying variables (high BLVs).

  4. The Boundary Membership Value (BMV) describes the status of candidate BEs. For crisp boundaries, locations are either a member of the boundary set (BMV = 1), or not (BMV = 0). Fuzzy wombled boundaries can have values of 0 or 1, or any value in between. For fuzzy boundaries, any location with a value above 0 is considered a BE. See also: Crisp vs. fuzzy wombled boundaries.

  5. A subboundary is a group of connected boundary elements; one or several subboundaries may comprise an entire boundary.

See also: